Three new nuclear genes, sigD, sigE and sigF, encoding putative plastid RNA polymerase σ factors in Arabidopsis thaliana

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Abstract
Three new nuclear genes (sigD, sigE and sigF) of Arabidopsis thaliana, encoding putative plastid RNA polymerase σ factors, were identified and analyzed. Phylogenetic analysis revealed that higher plant σ factors fell into at least four distinct subgroups within a diverse protein family. In addition, Arabidopsis sig genes contained conserved chromosomal intron sites, indicating that these genes arose by DNA duplication events during plant evolution. Transcript analyses revealed two alternatively spliced transcripts generated from the sigD region, one of which is predicted to encode a σ protein lacking the carboxy-terminal regions 3 and 4. Finally, the amino-terminal sequence of the sigF gene product was shown to function as a plastid-targeting signal using green fluorescent protein fusions.